This invention relates to internal signal path selecting techniques used in an audio reproducing apparatus. More particularly, the invention relates to suitable techniques for selecting one of an analog audio signal and a digital audio signal as an audio signal to be outputted from an AV (Audio Visual) control amplifier in a case where, for example, one AV apparatus is connected to the AV control amplifier so that both an analog audio signal and a digital audio signal are inputted from the AV apparatus into an analog input terminal and a digital input terminal respectively of the AV control amplifier.
AV apparatus, such as a DVD player, a video tape recorder and a TV receiver with built-in BS digital tuner configured so that both an analog audio signal and a digital audio signal can be outputted therefrom are being spread. Therefore, a recent AV control amplifier is provided with both an analog input terminal and a digital input terminal respectively. When both an analog audio signal and a digital audio signal are inputted from an AV apparatus into the analog input terminal and the digital input terminal respectively, a signal path corresponding to the analog audio signal or a signal path corresponding to the digital audio signal is selected, and an audio signal transmitted through the selected signal path is reproduced and outputted.
For example, a case where the AV apparatus is a TV receiver with built-in BS digital tuner will be discussed. At present, the TV broadcasts include a terrestrial broadcast, a BS analog broadcast and a BS digital broadcast.
In a BS digital broadcast, a video signal is changed from a video signal of an analog system adopted in a BS analog broadcast to a video signal of a MPEG-2 system, which is a digital compression system, and an audio signal is changed from a digital PCM (Pulse Code Modulation) signal adopted in a BS analog system to a MPEG2 AAC (MPEG2 Advanced Audio Coding) signal, which is a signal of a digital audio compression system. The MPEG2 AAC can transmit a multi-channel audio signal in a compressed state. Therefore, unlike a 2-channel reproduction of a digital PCM signal in a BS analog broadcast, an audio reproduction having a full of realism can be obtained in a motion picture and the like.
Since a BS digital broadcast has been started, and a BS analog broadcast is scheduled to terminate the service, a case where a terrestrial broadcast and a BS digital broadcast are handled as TV broadcasts will be described.
In order to receive a terrestrial broadcast and a BS digital broadcast to reproduce a video signal and an audio signal, it is necessary to use a so-called TV receiver with built-in BS digital tuner in which a tuner for a BS digital broadcast is built-in tuner together with a tuner for a terrestrial broadcast.
When receiving a terrestrial broadcast, TV receiver with built-in BS digital tuner receives the broadcasting waves by the tuner for terrestrial broadcast and demodulates the same, and then displays the motion picture corresponding to the video signal thus-obtained on a TV screen. The audio signal is outputted from built-in loudspeakers, or from the loudspeakers connected to an AV control amplifier whose analog input terminal is connected to an analog output terminal of the TV receiver.
When receiving a BS digital broadcast, the TV receiver with built-in BS digital tuner receives the BS digital broadcasting waves and demodulates the same by the tuner for BS digital broadcast, and displays the motion picture corresponding to the video signal thus-obtained on a TV screen. The audio signal is outputted from a built-in 2-channel loudspeakers, or from loudspeakers connected to the AV control amplifier whose digital input terminal is connected to digital output terminal of the TV receiver. The audio signal outputted from the digital output terminal of the TV receiver with built-in BS digital tuner is a MPEG2 AAC signal. Therefore, the AV control amplifier connected to the TV receiver with built-in BS digital tuner is necessary to be an AV control amplifier capable of decoding the MPEG2 AAC signal. The AV control amplifier decodes the MPEG2 AAC signal outputted from the TV receiver with built-in BS digital tuner, and outputs a multi-channel audio signal thus-obtained, from the loudspeakers connected to this AV control amplifier.
In order to make the AV control amplifier operate the audio signal thus outputted from the TV receiver with built-in BS digital tuner supporting both a terrestrial broadcast and BS digital broadcast, it is necessary to provide both an analog input terminal and a digital input terminal on the AV control amplifier to which both an analog output terminal and a digital output terminal of the TV receiver with built-in BS digital tuner are connected respectively. It is also necessary to switch the internal signal path in the AV control amplifier in accordance with a decision whether to reproduce and output an analog audio signal for a terrestrial broadcast inputted into the analog input terminal, or to reproduce and output an MPEG2 AAC signal for a BS digital broadcast inputted from the digital input terminal.
A first method of selecting a signal path in an AV control amplifier is disclosed in JP-A-11-289594. In this method, a user is made to select between a signal path corresponding to an analog audio signal and a signal path corresponding to a digital audio signal, and to input the selection through an operating unit of an AV control amplifier into a certain AV apparatus, and inputted selection is stored in the AV control amplifier. In order to reproduce and output an audio signal from the same AV apparatus, a signal path is always selected in accordance with the inputted selection stored in the AV control amplifier.
Another method of selecting a signal path in an AV control amplifier is the following method. Namely, in the case where both an analog input terminal and a digital input terminal provided for an AV control amplifier are connected to an analog output terminal and a digital output terminal of the same (one) AV apparatus respectively, when a digital audio signal is inputted into the digital input terminal, this digital audio signal is subjected to DA conversion by a digital to analog (DA) converter in the AV control amplifier irrespective of the condition of the analog input terminal. An analog audio signal thus obtained is outputted from loudspeakers connected to this AV control amplifier.
In this second method, a digital audio signal inputted from the digital input terminal is preferentially outputted. This is based on a general view that an audio signal obtained from a digital audio signal is less influenced by a transmission path than an audio signal obtained from an analog audio signal, and has a higher sound quality.
A third method of selecting a signal path in an AV control amplifier is disclosed in JP-A-2000-331431. In this method, an AV control amplifier receives information indicating the type of a digital audio signal from a DVD player, and switches an input system according to the received information. Namely, the DVD player (audio reproducing unit) identifies the type of a digital audio signal, which is recorded on the DVD, based on the data recorded thereon, and transmits information indicating the identified type of digital audio signal to an AV control amplifier (amplifier unit) through a transmission-reception unit. The AV control amplifier then determines based on the information indicating the type of digital audio signal received from the DVD player whether or not the digital audio signal inputted from the DVD player thereinto is a digital audio signal capable of being decoded by the AV control amplifier itself. Consequently, when the digital audio signal is determined as decodable digital audio signal, a signal path is switched so as to make AV control amplifier decode the digital audio signal inputted from the DVD player and output the signal thus-obtained. When the digital audio signal is determined as a non-decodable digital audio signal, the signal path is switched so as to make AV control amplifier output the analog audio signal inputted from the DVD player.